PDCD1 and gastric carcinoma: Finally, SHP2 mediates activation of immune checkpoint pathways, such as programmed cell death 1 (PD-1), B and T lymphocyte attenuator (BTLA), cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) and signal regulatory protein alpha (SIRPalpha) [16], [17], [18] and it is involved in the induction of gastric carcinoma by H. pylori[19], [20].